1. Field of the Invention
The present invention relates to a method of producing an image forming apparatus provided with an electron source and an image forming member (for example, fluorescent substance) for forming an image by irradiation with an electron beam emitted from the electron source, in a vacuum container, and to a process for forming a getter for use in such image forming apparatus.
2. Related Background Art
In an apparatus for displaying an image by irradiating a fluorescent substance constituting an image display member with an electron beam emitted from an electron source to cause light emission of the fluorescent substance, the interior of the vacuum container containing the electron source and the image forming member has to be maintained at high vacuum. This is because, if the pressure in the vacuum container is elevated by gas generation, although the effect extent of the gas is different depending to the kind of the gas, such gas disadvantageously affects the electron source to lower the amount of emitted electrons, whereby bright image display cannot be attained. Also the generated gas may be ionized by an electron beam to generate ions and the ions are accelerated by the electric field for accelerating electrons to collide with the electron source, thereby leading to the destruction of the apparatus.
The vacuum container of the image display apparatus is generally formed by combining glass members and adhering the joint portions thereof with frit glass or the like, and once the adhesion is completed, the internal pressure is maintained by a getter provided in the vacuum container.
In the ordinary cathode ray tube (CRT), an alloy composed of Ba as a main component is heated by supplying an electric current or a high frequency wave in the vacuum container to form an deposited film on the inside wall of the container, and high vacuum state is maintained by absorbing the internally generated gas with the deposited film.
On the other hand, there is being developed a plat panel display employing an electron source and a plurality of electron emitting devices arranged on a plat substrate. In such apparatus, the volume of the vacuum container becomes smaller in comparison with that of the CRT while the area of the gas-emitting wall does not decrease, so that the gas generation of a similar level results in a larger rise in the pressure in the container, thereby causing a severer influence.
Also in case of CRT, the vacuum container is provided therein with sufficient wall portions where the electron source or the image display member is absent, and the above-mentioned getter material can be deposited on such wall portions. On the other hand, in case of the flat panel display, the internal wall of the vacuum container is mostly occupied by the electron source and the image forming member. When the deposited-type getter film is attached on the occupied area to cause disadvantageous effects such as short-circuit of the wirings, so that the location of the getter film to be formed is limited.
For this reason, there has been considered utilizing the corner or the like of the vacuum container as the area for forming the getter film, thereby avoiding the deposition of the getter material on the portion constituted by the image forming member and the electron source (hereinafter, referred to as xe2x80x9cimage display areaxe2x80x9d). But, if the flat panel display exceeds a certain size, there cannot be secured a sufficient area of the deposited getter film in comparison with the gas discharge amount.
In order to solve the above drawbacks and to secure a sufficient area of the getter, there has been proposed a method (Japanese Patent Application Laid-Open No. 5-151916) of providing, as shown in a cross-sectional view of FIG. 3 showing a portion concerning the getter treatment of a conventional flat image display apparatus, a wire getter 1008 on an outside, for example, along the external peripheral portions, of the image display area between a fluorescent substance 1006 and a field emittion device 1007 provided opposite to each other in an external container 1005, thereby depositing and forming a getter film 1009 on the side surface of the external peripheral portion, a method (Japanese Patent Application Laid-Open No. 4-289640) of attaching, as shown in a cross-sectional view of FIG. 4 showing a portion concerning a getter treatment of a conventional flat image display apparatus, a getter chamber 1015 containing a getter material 1018 for forming the getter film, at a side of a space formed by a face plate 1014 and a rear plate 1012, and a method (Japanese Patent Application Laid-Open No. 1-235152) of providing a space between an electron source substrate and a rear plate of a vacuum container and forming the getter material therein.
In addition to the aforementioned drawbacks, the gas generation in the vacuum container of the flat image display apparatus causes a drawback that a pressure easily increases in a local position. In the image display apparatus having the electron source and the image display member, the gas generation in the vacuum container principally takes place in the image display area irradiated with the electron beam.
In the conventional CRT, since the image display member and the electron source are mutually separated and the getter film formed on the internal wall of the vacuum container is positioned therebetween, the gas generated in the image display member widely diffuses until is reaches the electron source, and a part of the gas is adsorbed by the getter film, so that the pressure does not rise extremely at the position of the electron source. Also an extreme local pressure rise is not caused by the gas discharged from the electron source itself, since the getter film is also provided around the electron source.
In the flat image display apparatus, however, the image display member and the electron source are closely positioned, so that the gas generated from the image display member reaches the electron source before diffusing sufficiently, thereby inducing a local pressure rise. Particularly in the central portion of the image display area, the local pressure rise tends to appear larger in comparison with the peripheral portion, because the gas cannot diffuse to the area of the getter film. The generated gas is ionized by the electrons emitted from the electron source, thereby causing damage between the electron source and the image display member or inducing a discharge to destroy the electron source.
In consideration of the foregoing, there is already disclosed a constitution of the flat image display apparatus having a specified structure, which comprises positioning a getter material in the image display area and immediately absorbing the generated gas. For example, Japanese Patent Application Laid-Open No. 4-12436 discloses a method, in an electron source having a gate electrode for taking out the electron beam, of forming the getter electrode with a getter material, and illustrates an electron source of field emission type having a conical projection as the cathode and a semiconductor electron source having a pn junction. Also, Japanese Patent Application Laid-Open No. 63-181248 discloses a method, in a plat panel display provided with an electrode (for example, grid) for controlling the electron beam between a group of cathodes and a face plate of the vacuum container, of forming a film of getter material on such control electrode.
Also, U.S. Pat. No. 5,453,659, entitled by xe2x80x9cAnode plate for flat panel display having integrated getterxe2x80x9d, issued on Sep. 26, 1995 to Wallace et al. discloses a structure of forming a getter member in the gap between the fluorescent substances on the stripes formed on the image display member (anode plate). In this example, the getter material is electrically separated from the fluorescent substance and the conductive member electrically connected thereto, and the getter is activated by giving a suitable potential to the getter and irradiating and heating the getter with the electrons emitted from the electron source.
The electron emitting device for use as the electron source in the flat panel display should naturally be simple in the structure and the producing method, in consideration of the production technology and the production cost. With respect to these points, the aforementioned electron source having the getter electrode formed of the getter material, disclosed in Japanese Patent Application Laid-Open No. 4-12436, requires complicated steps in the vacuum apparatus for forming the control cathode chip or for forming the semiconductor junction, and is limited in size by the production apparatus.
Also the apparatus having the control electrode etc. between the electron source and the face plate as disclosed in Japanese Patent Application Laid-Open No. 63-181248 is complicated in structure and involves complicated steps such as alignment of these components in the manufacture. Also the getter disclosed in Japanese Patent Application Laid-Open No. 8-225806 is formed by compressing the mixture of metal powder for forming the getter and a powdered organic compound and then sintering the compressed mixture at about 1000xc2x0 C. in vacuum or in inert gas, and therefore cannot be provided within the display panel in consideration of pressure and temperature required.
Also in the method of forming the getter material on the anode plate, disclosed in U.S. Pat. No. 5,453,659, the getter material and the fluorescent substance have to be electrically insulated, and the precise fine work is required for the above formation, and patterning by photolithographic technology is repeated. The above process therefore becomes complex, and the size of the apparatus to be employed for photolithography is limited.
The electron emitting device capable of satisfying the aforementioned requirement of easy production process can includes the lateral-shaped electron emitting device of field emission type and the electron emitting device of surface conduction type. The lateral-shaped electron emitting device of field emission type is composed, on a flat substrate, of a cathode having a pointed electron emitting portion and an opposed anode for applying a high electric field to the cathode, and can be produced by thin film deposition technology such as evapor deposition, sputtering or plating and ordinary photolithography. The electron emitting device of surface conduction type emits electrons by passing a current to a conductive film having a high resistance portion in one portion thereof, and an example of such device is disclosed in Japanese Patent Application Laid-Open No. 7-235255.
Since the electron source using these devices does not have the gate electrode of the shape as disclosed in Japanese Patent Application Laid-Open No. 4-12436 or the control electrode of the shape as disclosed in Japanese Patent Application Laid-Open No. 63-181248, the getter is to be provided outside the image display area by a method similar to those disclosed in these applications.
As already explained in the foregoing, the most significant source of gas generation is the image display member such as the fluorescent film receiving the impact of electrons of high energy, and the electron source itself. Naturally, gas generation can be prevented if there can be executed sufficient degassing by baking for a prolonged period at a high temperature or the like. In the practical apparatus, however, sufficient degassing can not be executed in some cases since the electron emitting device and other components are damaged thermally, so that the gas generation is highly probable.
In case the pressure of the generated gas is a relatively low, in addition to the influence on the electron emitting characteristics which is caused by absorption of the gas on the electron emitting portion of the electron source, it is afraid that the gas molecules ionized by the potential emitted by the electron source are accelerated by the electric field formed by the voltage applied between the image display member and the electron source or between the positive electrode and negative electrode of the electron source, and then collide with the positive electrode or negative electrode of the electron source, thereby causing damage thereon.
Also in case the gas pressure is elevated locally or instantaneously, it is afraid that the ions accelerated by the electric field collide with other gas molecules to generate ions in succession and eventually induce a discharge. In such case, it is afraid that the electron source is partially broken, resulting deterioration of the electron emitting characteristics. Also the gas generation from the image display member is caused by abrupt release of gas, such as H2O, H2, CH4, CO, CO2, O2 etc., contained in the fluorescent substance when electrons are emitted to conduct the light radiation of fluorescent substance after the image display apparatus is completed. Such gas generation may result in a phenomenon of evident drop of the image luminance in the initial driving stage of the apparatus.
By continuing the driving thereafter, gas is generated also from the area around the electron source, whereby the characteristics gradually deteriorate. In the conventional case where the getter area is provided outside the image display area, the gas generated in the central portion of the image display area not only requires a time for reaching the outside getter area but also is re-adsorbed by the electron source before being absorbed by the getter, whereby the getter is unable to be effective enough for preventing the deterioration in the electron emitting characteristics and the decrease of the image luminance may become conspicuous particularly in the center of the image display area.
Consequently, in the flat image display apparatus of the structure without the gate electrode or control electrode, there has been desired a novel structure in which the getter member can be positioned within the image display area so that a generated gas is rapidly removed. It has also been desired to form the getter at a low temperature, in consideration of the damage to the components in the vicinity of the getter member.
In consideration of the foregoing, an object of the present invention is to provide an image forming apparatus capable of solving the aforementioned drawbacks, particularly an image forming apparatus equipped with a getter of high performance, less variation in luminance with the lapes of time and less luminance fluctuation. Another object of the present invention is to provide a process for forming a getter at a low temperature that does not damage other elements and at an arbitrary position in a simple manner with a low cost, thereby being adaptable to various processes.
According to the present invention, there is provided a process for forming a non-evaporative getter, comprising forming the non-evaporative getter by a gas deposition method.
According to the present invention, there is provided a process for forming a non-evaporative getter, which comprises generating metal particles by heating in an inert gas atmosphere in a particle generating chamber, conveying the metal particles through a conveying pipe to a film forming chamber by a pressure difference and discharging the metal particles onto a substrate to form the non-evaporative getter on the substrate.
According to the present invention there is also provided a method of producing an image forming apparatus provided with an electron source, and an image forming member for forming an image by irradiation with an electron beam emitted from the electron source, and a non-evaporative getter in a container, which comprises forming a non-evaporative getter by a gas deposition method.
According to the present invention, there is further provided a method of producing an image forming apparatus provided with an electron source, an image forming member for forming an image by irradiation with an electron beam emitted from the electron source and a non-evaporative getter in a container, which comprises forming the getter on a substrate by generating metal particles by heating in an inert gas atmosphere in a particle generation chamber, conveying the metal particles through a convey pipe to a film forming chamber by a pressure difference, and discharging the metal particles onto the substrate.